The object of the present invention is a surfaced wood-based board which is of the type presented in the preamble to the adjoining claim 1. Another object of the invention is a method for surfacing a wood-based board which is of the type presented in the preamble to the adjoining claim 11.
It is known to surface wood-based boards, such as plywood, particle board, fibreboard or other board, for example board made of sawn timber, with plastic surfacing to improve their surface properties, such as wear resistance or moisture resistance. In such case the surfacing film should be durable, but, however, should adhere strongly to the surface of the wood-based material.
Wood-based surfaced boards are used, for example, in the transport vehicle industry as wall and floor material for various cargo spaces, in the walls of moulds for casting concrete, and for other purposes Many thermoplastics are promising in that a suitable surfacing material can be chosen from among them according to the characteristics required from the product when it is used. Thermoplastics can also be worked using heat, and they can be melted/softened and solidified by adjusting the temperature, by means of which they can also be made to adhere to various surfaces. Thermoplastics can also be worked when molten, which enables them to be spread on surfaces by means of extrusion, and allows the forming of various profiles.
The problem of thermoplastics concerns their adhesion to substrates such as wood or wood-derived products. The high melt viscosity of the thermoplastics that are most frequently used makes it more difficult to attach the films by means of extrusion to the surface of wood. In addition, the unevenness of the substrate and the moisture contained by it may make it difficult to attach the film. Methods for surfacing wood-based boards with thermoplastic polymer particularly to improve the adhesion of the films are presented, for example, in Finnish patent 80637 and U.S. Pat. Nos. 3,544,669 and 4,143,187.
Similarly, a method for producing plastic/plywood composite is known from the international publication WO 96/32257, in which the surface of the plywood is subjected to special treatment (drying and crushing of the surface cells), after which a plastic film, such as a polyester film, surfaced with thermoplastic acting as a hot-melt adhesive can be affixed to the surface of the plywood with heat and pressure.
The aim of the invention is to present a surfaced wood-based board that does not require pre-treatment the substrate, but which can be surfaced with surfacing materials of various types containing thermoplastic, where the outermost surface of the surfacing materials can be chosen according to the demands of the application. For achieving this aim, the board relating to the invention is characterised mainly by what is presented in the characterising part of the adjoining claim 1. The surfacing has been provided by gluing a polyamide film to the surface of the substrate with a reactive adhesive layer. Polyamide film functions as a good substrate for other layers, for example, polyolefin layers, whereas a reactive adhesive, which most preferably has been absorbed in the carrier to form a uniform adhesive film, has good adhesion both to a wood-based substrate and to polyamide polymer.
As regards other preferred embodiments, reference is made to the adjoining dependent claims and the specification presented below.
Another aim of the invention is to present a method for surfacing wood-based board. For achieving this aim, the method is mainly characterised by what is presented in the characterising part of the adjoining claim 11. A crucial stage of the method is the gluing of the polyamide film to the wood-based substrate by means of a reactive adhesive layer. In the method, the polyamide film can function as a carrier for other, outer layers, and the method can be implemented by means of work methods known from wood laminating technology, particularly by means of hot-pressing. In addition, the formation of the surface can be carried out in one or more stages.
As regards other preferred embodiments of the invention, reference is made to the adjoining dependent claims and the specification presented below.